The embodiment relates to a light emitting device, a light emitting device package, and a lighting system.
A light emitting device (LED) includes a p-n junction diode having a characteristic of converting electric energy into light energy. The p-n junction diode can be formed by combining group III and group V elements of the periodic table. The LED can represent various colors by adjusting the compositional ratio of compound semiconductors.
When forward voltage is applied to the LED, electrons of an n layer are combined with holes of a p layer, so that energy corresponding to an energy gap between a conduction band and a valance band may be generated. This energy is realized as heat or light, and the LED emits the energy in the form of light.
A nitride semiconductor represents superior thermal stability and wide bandgap energy so that the nitride semiconductor has been spotlighted in the field of optical devices and high-power electronic devices. In particular, blue, green, and UV light emitting devices employing the nitride semiconductor have already been developed and extensively used.
The LED is divided into a lateral type LED and a vertical type LED according to the position of an electrode.
In the lateral type LED, a light emitting structure is formed on a thermal conductive substrate and two electrode layers are aligned over the light emitting structure.
Meanwhile, in the lateral type LED, a thick thermal conductive substrate is located at a lower end of the light emitting structure and a great amount of light is emitted through a lateral side of an insulating substrate, the function of a reflective layer located at a lower end of the insulating substrate is very important.
However, according to the related art, the reflective layer located at the lower end of the insulating substrate is includes a metal layer which represents weak reliability. That is, the reflectance of the metal layer may be degraded as time elapses, so that quantity of the light may be reduced.